Carbon nanotubes, multiwalled carbon nanotubes (MWNT) as well as single walled carbon nanotubes (SWNT), are currently attracting scientific and technological attention due to their fascinating properties and emerging applications [Baughman R. H. et al.: Science 297 (2002) 787]. As-prepared SWNT tend to assemble into bundles or ropes arranged in a close packed lattice or network. Inter-tube interactions within the bundles are dominated by van der Waals interactions of high cohesive energy rendering them inseparable [Girifalco L. A. et al.: Physical Review B (PRB) 62, 19 (2000) 13104]. Multilevel aggregation of the tubes results in low solubility and low dispersability of carbon nanotubes (CNT), affects their mechanical and electronic properties, and acts as an obstacle for most applications. For example, utilization of CNT as conducting fillers in polymeric matrices might benefit from their high length-to-diameter ratio (aspect ratio), which theoretically enables low percolation threshold (lowest CNT concentration still providing a conductive material); however, observed percolation thresholds are usually higher than expected due to aggregation of tubes.
Several methods, designed to reduce the short-range attraction between adjacent tubes, have been tried for dispersing and exfoliating the bundles of CNT. Some of the methods were shown to lead to exfoliation of bundles of SWNT in addition to dispersion of ropes. The methods include chemical modifications [Chen J. et al: Science 282 (1998) 95; Boul P. et al.: Chem Phys. Lett. 310 (1999) 367], surfactant adsorption [Vigolo B. et al.: Science 290 (2000) 1331; Wang J. et al.: J. Am. Chem. Soc. 125 (2003) 2408; Moore V. C. et. al.: NanoLetters 3, (2003) 1379], preparation of CNT/polymer composites, and adsorption of homopolymers onto CNT [Star A. et al.: Angew. Chem. Int. 40 (Ed. 2001) 1721; Chen J. et al.: Am. Chem. Soc. 124 (2002) 9034; O'Connel M. J. et al.: Science 297 (2002) 593]. The said methods comprise several disadvantages. It was, for example, shown that covalent modification often leads to impairing of mechanical and electrical properties of CNT [Garg A. and Sinnott S. B.: Chem. Phys. Lett. 295 (1998) 273], and to a change in the electronic structure [Chen J. et. al.: Science 282 (1998) 95]. In addition, methods that rely on surfactants are restricted to low concentrations of CNT [Vigolo B. et al.: Science 290 (2000) 1331]. Thus, surfactant-CNT suspensions usually contain a low concentration of individual tubes, along with a low concentration of ropes and bundles of CNT [Bandyopadhyaya R. et al.: Nano Letters, 2(1) (2002) 25]. It is therefore an object of this invention to provide a method for exfoliation of carbon nanotubes, that enables a sufficient concentration of suspended, de-agglomerated CNT, leading to the formation of stable dispersions, while preserving their unique properties. WO 02/076888 describes a method for the preparation of a suspension of CNT, comprising water-soluble polymers, providing stable dispersions of carbon nanotubes of high concentrations, said stable dispersion being an aqueous suspension. It is therefore a further object of this invention to provide a method for the preparation of stable, concentrated suspension of carbon nanotubes comprising a polymer, in general environment, such as aqueous media or organic solvents.
It is still another object of this invention to provide a method for exfoliating and dispersing carbon nanotubes and store them in a ready-to-use powder form.
It is a further object of this invention to provide a method for dispersing carbon nanotubes, comprising a polymer that can act as a compatibilizer for suitable contact between said tubes and their microenvironment.
Other objects and advantages of present invention will appear as description proceeds.